Date of Award

Spring 2019

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Lynn M Kister

Second Advisor

Christopher G Mouikis

Third Advisor

Charlie J Farrugia

Abstract

Coronal mass ejections (CMEs) and corotating interaction regions (CIRs) are the most common drivers of geomagnetic storms, influencing the dynamics of the inner magnetosphere and the response of the radiation belts. The main outer radiation belt acceleration mechanisms are inward radial diffusion and local acceleration by chorus waves, while magnetopause shadowing and by pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves and other wave modes are the main true loss mechanisms. The link between these mechanisms and the solar interplanetary structures is the ring current response to these drivers. The different characteristics of the two solar wind drivers, CMEs and CIRs, will affect the convection electric field and the nightside plasma sheet environment differently, which will affect the ion and electron ring current development. This dissertation studies the spatial and temporal development of the storm-time ring current, the generation of EMIC and chorus waves, and the effect that the chorus waves have on the re-development of the outer radiation belt for the two types of storm drivers. We have taken advantage of the wide range of particle and fields observations provided by the Van Allen Probes mission and conducted four studies which characterize the response of the storm-time inner magnetosphere within this framework. In these studies, we have determined the development of the storm-time ring current and the effect of the ion composition, the development of EMIC and whistler-mode chorus waves, and the outer radiation belt response to the development of chorus waves and the seed (100s of keV) electrons. We have shown that during geomagnetic storms, the enhancement of the convection electric field provides access for the low energy (< 60 keV) ions and electrons to the inner magnetosphere which generate the storm-time ring current via adiabatic transport from the nightside plasma sheet. Since the transport of the storm-time ring current comes from the nightside plasma sheet, differences (due to the different storm drivers) in the conditioning of the plasma sheet affect the development of the storm-time ring current. Additionally, using a linear theory proxy to estimate wave growth, we have shown that the enhancement of < 60 keV ions affect the development of electromagnetic ion cyclotron waves (EMIC) and the < 60 keV electrons impact the whistler-mode chorus wave growth, both of which impact the outer radiation belt. We found that the storm-time development of EMIC and chorus wave activity is storm phase and local time dependent, and it depends on the access and drift history of the < 60 keV ions and and electrons, respectively. Lastly, we have shown that while chorus wave activity is a feature of the main phase due to the enhancement of the convection electric field, the timing, intensity, and depth of enhancement for the seed electron population is crucial for the re-development and enhancement of the outer radiation belt via local acceleration, and that CME-driven storms are more likely to generate radiation belt enhancements due to their ability to provide such a seed electron enhancement.

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